The present invention relates to a circuit for controlling light-emitting diodes (LEDs).
In order to improve traffic safety during darkness, active and passive light elements are often used for identifying humans and also animals. Besides passive light elements like for example reflectors, active light elements are also used, which are often configured as battery- or accumulator operated LED units. In conventional battery operated light- and signal elements, however, there is an issue that, on the one hand, sufficient, constant and reliable illumination needs to be provided, and on the other hand, the weight of the light element needs to be limited.
An embodiment of a conventional light- and signal element and a circuit for controlling the LEDs is described in EP 1 536 390 A1. The light- and signal element, which is in particular usable as a collar for animals, includes a motion detector so that the LED module is turned on when a movement is detected in the periphery or when the LED module moves itself. This prevents the LED module from being illuminated when it is not in use in order to save energy and increase reliability.
However, there is an additional problem in that the energy provided in the batteries or accumulators is only partially used. The reason is that a forward voltage of the LEDs varies in a range of 1.6 V-3 V, depending on the color, so that the batteries or accumulators can only be discharged to a threshold voltage which corresponds to the amount of the forward voltage of the LEDs. Thus, an energy source is required which puts out a suitable voltage over a longer time period.
However, using powerful energy sources also increases the weight of the light- and signal element.
Furthermore, conventional battery operations of light- and signal elements have the disadvantage that the light intensity of light- and signal elements with identical configurations is highly variable, since also the forward voltage of LEDs with identical color is highly variable from batch to batch. This fact has proven to be a problem since no reliable illumination can be provided with a minimum light intensity of the light- and signal element.
Another problem of the prior art is that the light intensity of the light- and signal element continuously decreases for conventional battery operations with increasing operating time. Additionally, prior art circuits also use current in standby mode or hibernation, so that the batteries are depleted after a few weeks or months while the light element is not being operated.